1. Field of the Invention
The present invention relates to an inspection method and inspection device for inspecting the inner surface of a nozzle provided in a reactor vessel of a nuclear power plant.
2. Description of the Related Art
For example, a nuclear power plant having a pressurized water reactor (PWR) uses light water, which serves as primary cooling water, as a reactor coolant and neutron moderator, and makes it into a high-temperature and high-pressure water that does not boil throughout the reactor internal, and causes the high-temperature and high-pressure water to flow into a steam generator, so that steam is generated by heat exchange, and this steam is caused to flow into a turbine generator to generate power.
In such nuclear power plant, various kinds of structural objects in the pressurized water reactor are required to be inspected with a regular interval in order to ensure sufficient level of safety and reliability. When each inspection is carried out, and a defect is found, then the required portions related to the defect are repaired. For example, in the pressurized water reactor, the main body of the reactor vessel has an outlet nozzle for providing the primary cooling water to the steam generator and an inlet nozzle for retrieving the primary cooling water of which heat has been exchanged by the steam generator. These nozzles are connected, by means of welding, with the primary cooling water tube which is in communication with the steam generator. Since the nozzles and the primary cooling water tube are made of different materials, safe-end tubes are connected therebetween by means of welding.
With a cutting method and a cutting device for an inner surface of a nozzle of a reactor vessel as described in Patent Literature 1 (Japanese Patent No. 4444168), when a welded portion of the nozzle is determined to have defective surface such as crack due to secular change, a cutting device is inserted into the inside of the nozzle, and is positioned at a cutting position, and the cutting device cuts the welded portion. During the cutting process, the cutting position is determined with an eddy-current flaw detection sensor, and the inner surface shape of the nozzle is recorded with a displacement detection sensor, and the inner surface of the nozzle is cut on the basis of such data.
Patent Literature 1 indicates that the inner surface of the nozzle of the reactor vessel is repaired, and the device is hoisted by a crane and is inserted into the nozzle, and the cutting position is determined with the eddy-current flaw detection sensor. When the eddy-current flaw detection sensor is calibrated in such repairing method, the device is needed to be calibrated on a work floor of a nuclear reactor building of a nuclear power plant before the device is inserted into the inside of the nozzle, and thereafter, the device is needed to be hoisted by a crane and inserted into the inside of the nozzle, and the cutting position is determined with the eddy-current flaw detection sensor at that position, and thereafter, the device is needed to be hoisted by the crane to bring the device back to the work floor, and the device is needed to be calibrated. In this case, as described above, the reactor vessel forms a loop having the inlet nozzle and the outlet nozzle and connected to one steam generator. Alternatively, in a nuclear power plant having multiple steam generators, the reactor vessel includes multiple inlet nozzles and outlet nozzles so as to form as many loops as the number of steam generators. More specifically, it is necessary to perform the work for the multiple nozzles, which includes hoisting the device with a crane and inserting the device into the inside of the nozzle, and returning the device back to the work floor, and therefore, it takes a lot of time and the work efficiency may be reduced.
In an under-water eddy-current test device described in Patent Literature 2 (Japanese Laid-open Patent Publication No. 7-218474), a test coil and a normal coil are attached to an operation head that moves in the upper/lower vertical direction along a fixed fuel rod and that moves in the forward/backward direction and the horizontal direction perpendicular to the upper/lower vertical direction, and a sensitivity calibration test piece is provided in proximity thereto. During the measuring process, the test coil is pushed out to the forward position, and is brought into contact with the fuel rod. On the other hand, when the sensitivity of the test coil is calibrated before the measurement process, the sensitivity calibration test piece is fixed with respect to the horizontal direction movement of the operation head, and the test coil is moved in the horizontal direction, so that it is brought into contact with the sensitivity calibration test piece in a face to face manner.
An eddy-current inspection device for fuel cladding described in Patent Literature 3 (Japanese Patent No. 3378500) includes a chuck unit for holding a fuel cladding, a sensor holder unit for pushing an inspection sensor against the center of the fuel cladding so as to be perpendicular thereto, and a zero calibration test piece unit for an inspection sensor, wherein the zero calibration test piece unit includes a rotation mechanism, and during the calibration process, it is provided to be able to move to the forward side of the inspection sensor.
In Patent Literature 2 and Patent Literature 3, the calibration test piece is provided on the device, and therefore, the calibration can be performed in the under-water environment where the inspection is performed. However, in Patent Literature 2, during the measurement process, the test coil is pushed forward to be in contact with the fuel rod, and when the sensitivity of the test coil is calibrated, the test coil is moved in the horizontal direction, and is brought into contact with the sensitivity calibration test piece in a face to face manner. For this reason, the position of the test coil may be out of the position where it faces the fuel rod, and when each environment has changed, the calibration may not be performed accurately. In Patent Literature 3, the zero calibration test piece unit has the rotation mechanism and is arranged to be able to move to the forward side of the inspection sensor during the calibration process. Therefore, when the device is arranged at the position where the inspection is performed, the zero calibration test piece unit cannot be arranged at the forward side of the inspection sensor, and therefore, as a result, during the calibration process, the position of the device needs to be changed from the forward side of the fuel cladding, and the environment would be changed, which may make it impossible to accurately perform the calibration.